1. Field of the Invention
The present invention relates to a capacitive occupant sensor.
2. Description of Related Art
JP-A-2008-203150 discloses a capacitive occupant detecting system to detect an occupant seated on a vehicle seat. The system has a sensor portion arranged on a seat face of the vehicle seat.
The sensor portion includes a main part having a silver electrode and a carbon electrode. The silver electrode is arranged on a base film, and is further used as a wiring. The carbon electrode is arranged on the base film so as to cover the silver electrode. Material cost of the silver electrode is higher than that of the carbon electrode. A plane structure of the base film has a rectangular frame shape, and the silver electrode of the main part is formed to correspond to the plane structure of the base film.
A capacitance variation of the sensor portion is detected by the system. Thus, it is detected whether an occupant is seated on the vehicle seat.
The main part of the sensor portion is constructed by the carbon electrode and the silver electrode. The silver electrode is more expensive than the carbon electrode. If an amount of the carbon electrode is increased so as to reduce a cost of the main part, a resistance of the main part becomes large. If an amount of the silver electrode is increased so as to reduce the resistance of the main part, the cost of the main part becomes high.